body {
  font-family: Arial, sans-serif;
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  height: 100vh;
  margin: 0;
  background-color: #f0f0f0;
}
h1 {
  margin-bottom: 20px;
}
.game-board {
  display: grid;
  grid-template-columns: repeat(4, 100px);
  grid-gap: 10px;
}
.card {
  width: 100px;
  height: 100px;
  background-color: #3498db;
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: 2rem;
  color: white;
  cursor: pointer;
  border-radius: 10px;
  user-select: none;
  transition: transform 0.3s;
}
.card.flipped {
  background-color: #2ecc71;
  transform: rotateY(180deg);
}
.card.matched {
  background-color: #95a5a6;
  cursor: default;
}
button {
  margin-top: 20px;
  padding: 10px 20px;
  font-size: 1rem;
}